Sulfasalazine (SSZ; salicylazosulfapyridine, salazopyrin, salazopyridine), 2-hydroxy-5-[2-[4-[(2-pyridinylamino)sulfonyl]phenyl]diazenyl]-benzoic acid, was first described in U.S. Pat. No. 2,396,145. Sulfasalazine forms brownish-yellow crystals. It has 4 theoretical pKa/b values, which are at 0.6, 2.4, 9.7 and 11.8, a water solubility of less than 0.05 mg/mL at ambient temperature and a melting point of 240 to 245° C. Sulfasalazine decomposes at a temperature of 260 to 265° C. The structure of sulfasalazine is shown below:

Sulfasalazine is known to be highly effective in the prevention, prophylaxis of progression, and/or treatment of several different autoimmune diseases, for example rheumatoid arthritis, juvenile idiopathic arthritis, ankylosing spondylitis, and ulcerative colitis. It is one of the most widely used small molecule disease-modifying antirheumatic drugs (DMARDs), either as stand-alone therapy or in combination with glucocorticoids and/or in combination with other small molecule DMARDs, such as methotrexate and/or hydroxychloroquine and/or biological DMARDs, such as anti TNF-alpha biologics (for example infliximab, golimumab and adalimumab).
Neither the mode nor site of action of sulfasalazine in autoimmune diseases, in which it has been found to be therapeutically effective, has been elicited with certainty. In addition, these diseases are of unknown aetiology. It is generally assumed that the therapeutic effect of sulfasalazine stems from its metabolite sulfapyridine (SP). However, it is to date unknown whether the ability of sulfasalazine to successfully treat autoimmune diseases stems from sulfasalazine itself, or partially to completely from its metabolites. Both non-clinical and clinical studies so far have failed to provide conclusive evidence in either direction.
In adults, guided by tolerability and efficacy, sulfasalazine is typically administered orally at dose levels of 500 to 6000 mg per day. Tablets contain 500 mg of the active pharmaceutical ingredient. Commercially available tablets include both immediate and modified release compositions, which are taken one to three times daily, typically about one hour prior to a meal to avoid food effects. The systemic bioavailability of sulfasalazine in man is low, only 15 to 20° of an oral dose is absorbed in the small intestine. Upon multiple dosing, steady state levels of sulfasalazine are reached within 24 hours.
The intra- and inter-variability of systemic levels of sulfasalazine and its major metabolites at a given dose level is high. For example, mean serum levels following oral administration of 4000 mg/day typically are between 10 and 15 ug/mL, with a Cmax at 4 to 12 h.
Sulfasalazine is subject to entero-hepatic clearance. Both non-absorbed and enterohepatically cleared sulfasalazine is transformed by aza-reducing gut flora to 5-aminosalicylic acid (which has a systemic bioavailability from 10 to 30°) and sulfapyridine (which has a systemic bioavailability of about 60°). Following the oral administration of sulfasalazine, these metabolites can be detected in the plasma after about 10 hours. In the liver, non-enterohepatically cleared sulfasalazine is also metabolized to 5-aminosalicylic acid and sulfapyridine, the latter one being associated with the common side effects like nausea, headache, dry mouth, vomiting and diarrhoea (Schroeder and Evans, Gut, 1972, 13, 278-284) seen in SSZ therapy.
The major hepatic metabolite of sulfapyridine is the acetylated form, which is formed through arylamine N-acetyltransferase 2 (NAT2). The rate of acetylation is genetically determined and follows a bimodal distribution. In 60° of the general population, the acetylation rate is slow, while in the remaining 40° of the general population, the acetylation rate is fast. Steady state levels of sulfapyridine and its acetyl-metabolite are reached after 72 h, with typical mean serum levels of 17 to 45 ug/mL for sulfapyridine and 8 to 21 ug/mL (25 to 62° of SP) of acetylated sulfapyridine (slow and fast acetylators, respectively). In slow acetylators, the steady state levels are reached sooner, which is accompanied by a faster onset of adverse events like nausea and vomiting (Schroeder and Evans, Gut, 1972, 13, 278-284). There is no difference in absorption characteristics, plasma protein binding (ca. 50°) or apparent distribution volume (0.9 L/kg) between fast and slow acetylators. However, the elimination half-life of sulfapyridine in slow acetylators (15.3 h) is almost three times longer than the elimination half-life in fast acetylators (5.5 h), and the total plasma clearance in fast acetylators (135.3 mL/min) is almost four times faster than in slow acetylators (36.9 mL/min) (Fischer and Klotz, Ther. Drug Monit. 1980, 2, 153).
In a retrospective study in rheumatoid arthritis (3 g/day for 24 weeks) similar efficacy rates of sulfasalazine were found, regardless of the acetylator phenotype. In a prospective study in rheumatic arthritis (RA) (24 weeks), fast acetylators treated with 3 g/day sulfasalazine showed a marked improvement in the overall clinical status, while the overall clinical status of slow acetylators, that were being treated with half of the SSZ dose, remained unchanged. However, the drop-out rates, due to nausea and vomiting, at the low treatment dose of 1.5 g/d, were three times greater in the slow acetylator group (Pullar et al, Ann. Rheum. Dis. 1985, 44, 831-837). In a prospective study in ankylosing spondylitis (AS) in Han Chinese patients, the prevalence and time of onset of SSZ-induced AEs were related to the polymorphic type of NAT1 and NAT2. The incidence of both overall and dose-related adverse events (AEs) were significantly higher in the NAT2 slow acetylator phenotype. The prevalence of drug termination in NAT2 slow acetylator patients was significantly higher than in fast acetylator patients. (Hou et al, BMC Pharmacol. Toxicol. 2014, 15, 64).
This is consistent with findings in studies in healthy volunteers, where in the different acetylator phenotype higher steady state levels of sulfapyridine correlate with the time of onset, the rate of occurrence and the perceived severity of side effects. In RA patients with a slow acetylation rate, the ratio found for the blood plasma steady state concentration (CSS) and the infinite area under the curve of plasma concentrations (AUC0→∞) of SP vs SSZ, when treated with 2 g/d of sulfasalazine, is 6 and 5.5, respectively (Rains et al, Drugs 1995, 50, 137-156). In a healthy volunteer study with a population of 63° slow acetylators, the ratio found for the AUC0→∞ of SP vs SSZ was 4.
Sulfasalazine is a substrate for the ABCG2 transporter protein, which is highly expressed at the apical membrane of both enterocytes in the gut lumen and hepatocytes in the liver. These tissues that are typically involved in both absorption and bioavailability (F) and/or disposition and/or biliary excretion (hepatic clearance) of drugs. The ABCG2 gene is subject to polymorphism, where the nucleotide changes from c.421C/C to C/A results in a reduced efflux activity. The incidence of this polymorphism is estimated to be between 7-11° in Caucasians, 26-35° in East Asians and less than 1° in Sub-Saharan Africans. Yamasaki et al (2008) demonstrated in healthy Japanese volunteers that, following oral administration of sulfasalazine, both ABCG2 and NAT2 gene polymorphisms play an important role in the pharmacokinetics of sulfasalazine, sulfapyridine and its acetylated metabolite Ac-sulfapyridine. The mean AUC0-48 and Cmax of sulfasalazine were significantly higher, and the mean CLtotal/F was significantly lower in subjects with at least one ABCG2-A mutant allele, which was independent of the NAT2 genotype. The pharmacokinetic values of sulfapyridine and its acetylated metabolite appeared to be dependent on both the NAT2 genotype and the ABCG2 genotype, however. Since total urinary and biliary recovery of sulfasalazine have been reported to be very low in humans, as supported by non-clinical data in portal-vein-cannulated rats (Matsuda et al. 2013), the contribution of the ABCG2 transporter protein to the biliary excretion of sulfasalazine is believed to be small.
The high affinity of sulfasalazine for the ABCG2 transporter and/or its poor water solubility are believed to contribute to the low systemic bioavailability of this drug. Therefore, relatively high oral dose levels of sulfasalazine are needed to reach sufficient systemic levels for it to be efficacious in the prevention, prophylaxis of progression, and/or treatment of autoimmune diseases, like rheumatoid arthritis. High oral dose levels and low systemic bioavailability of sulfasalazine drive the high systemic levels of its metabolite sulfapyridine (which causes its inherent side effects), as the unabsorbed sulfasalazine is converted to sulfapyridine in the lower intestinal tract and subsequently absorbed into the blood stream.
The high affinity of sulfasalazine for the ABCG2 transporter is of special importance in a setting of systemic inflammation, as is prevalent in the targeted diseases like rheumatoid arthritis. It is well known, that the pharmacokinetic profile of small molecules, like the currently marketed DMARDs, can be dramatically changed during the inflammation stage in autoimmune disease, which is due to altered expression levels of metabolizing enzymes and/or transporter proteins. This results in altered plasma levels and/or the volume of distribution of the parent compound and/or its metabolites, as compared to a non-inflammation situation prevalent in the general population and possibly in patients in remission. Polymorphisms in metabolizing enzymes and/or transporter proteins and/or co-administration of modulators of such metabolizing enzymes and/or transporter proteins also affect the pharmacokinetics of sulfasalazine and co-administered DMARDs in such patients, as compared to general patient populations. In consequence, the benefit/risk profile in a disease stage of significant inflammation may be different from the benefit/risk profile found during non- or low-inflammation stage and/or to the benefit/risk profile found in patients with polymorphisms in metabolizing enzymes and/or transporter proteins. Dosing and managing over-dosing and side effects are thus challenging when administering SSZ.
WO88/01615 discloses ester derivatives of carboxylic acid medicaments. These new derivatives provide the characteristic pharmacological response and are less irritating to mucosa than the acids from which they are derived, while the cleaved off moiety is of a non-toxic nature to humans. The bioavailability from the site of administration is faster in these esters compared to the original carboxylic acid medicaments. The exemplified medicaments are acute treatment medicaments, such as pain killers, for which faster absorption rates are highly preferred. However, the disclosure does not deal with the problem of increased absorption for medicaments that need to be administered repeatedly over a longer time period (chronic disease treatment) in diseases that, for example, are of an autoinflammatory nature, where the pharmacokinetics, i.e. absorption, maximum concentration in the blood stream (Cmax) and area under the curve (AUC), are known to differ during the acute disease flare as compared to disease remission, and for which the total amount of drug in the body from a given dose regimen, e.g. the AUC at steady state, needs to be increased in order to enhance the pharmacodynamic exposure to the carboxylic acid from which it is derived.
EP2418200 discloses new NSAID's phtalimide derivatives that aim to potentiate the anti-inflammatory and analgesic activity by acting synergistically on two fronts, i.e. by inhibiting the cyclooxygenase (COX) and inhibiting TNF-alpha. Preferably, esters and amides are obtained that are not usable in pharmaceutical compositions as prodrugs. A process is disclosed, wherein the phtalimide derivatives are obtained from prodrugs. It is unclear whether the compounds are to be understood as prodrugs of parent compounds or are parent compounds themselves. Two alkyl ester sulfasalazine-phatalimide derivatives, where X is —CH2—O— or —CH2CH2—O— are shown as compounds 58 and 59. It is well-known, that N-phtamimidoalkyl esters are chemically unstable at low pH and can be readily hydrolyzed in acidic conditions, such as the stomach. Other examples include a sulfasalazine-phtalimide derivative, where X is —NH— (compound 57), as well as sulfasalazine-phtalimide derivatives, where X is either a benzyl-O— or benzyl-alkyl-O— (compounds 60-63).
Sulfasalazine is not classified as an NSAID (non-steroidal anti-inflammatory drug) but is classified as a DMARD (disease modifying anti rheumatic drug). Further, sulfasalazine is itself an inhibitor of TNF-alpha. Therefore, a hybridization strategy to create a phtalimide derivative is neither needed nor logical. Besides, gastro-ulceration related to the carboxylic acid moiety of sulfasalazine can be overcome with the use of excipients that prevent the pharmaceutical composition from releasing sulfasalazine prior to reaching the intestinal tract. Such modified release forms of solid oral pharmaceutical compositions containing sulfasalazine are available on the market.
Pro-drugs of methyl hydrogen fumarate are used to treat multiple sclerosis and psoriasis. The intention of these pro-drugs is to reduce the lack of tolerance of fumarate treatments that stem from the wide spread and/or serious gastro-intestinal side effects that are believed to be caused by the carboxylic acid group of fumarates. In a broad range of known fumarate derivatives, US2010048651 discloses a new set of fumarate derivatives. A list of the chemical and enzymatic stability of a small selection of the compounds is disclosed. The compounds are tested under a limited range of conditions. However, the stability studies do not include the chemical stability at the relevant pH ranges that are found in the upper gastro-intestinal tract (pH 1-7.4) nor the stability in human-derived in vitro systems. The selected examples in US2010048651 do not clearly show that glycolamide derivatives of fumarates in general show a differentiated chemical or enzymatic stability as compared to other, structurally close derivatives of fumarates, especially not at pH 1-7.4 nor in human blood plasma. In addition, it is unclear how the absolute oral bioavailability of the disclosed compounds is different from dimethylfumarate itself (referred to in US2010048651 as 2), as results are being compared to a compound IV, which appears not to be disclosed in the patent application.
CA2951627 discloses prodrugs of naphthofuranes, specifically of Napabucasin (2-Acetyl-4H,9H-naphtho[2,3-b]furan-4,9-dione), which is described as compound (A). In compounds of general formula (IA) and (I), the CH3 group of the acetyl moiety of Napabucasin is derivatized with an ester function that carries substituent R2. R2 is an alkyl group that can by optionally substituted further with halogens, heteroatoms (N, O, S) and cyclic groups, and includes glycolamides (compounds 72 and 73). Following oral administration or incubation in plasma or liver microsomes, the 1-(R2)-3-oxo-3-naphthofuran-proprionates that are disclosed are positioned at the C2 position and converted to Napabucasin. This document shows that an acetyl function of a compound, when converted to a 3-oxo-1-(C1-6alkyl)-propionate, independent of the substitution pattern of the C1-6alkyl group, is metabolized by the body to the acetyl group, even when the C1-6alkyl contains a glycolamide (compounds 72 and 73). The formation of an acetyl group from a pro-drug instead of a carboxyl acid is not of interest as a pro-drug for sulfasalazine.
Beaulieu, et al, Bioorg Med Chem Lett, 2015, January, Vol 25, No 2, pp 210-215, discloses a wide range of ionizable and non-ionizable C1-4alkyl esters of the parent compound 2, in which the alkyl moiety is optionally substituted with halogen (Cl, P) or heteroatoms (N, O) or cyclic substituents, including glycolic amide substituents. The parent compound has a limited lipid solubility. The lipid solubility is improved in several ester analogues of the parent compound, including some, but not all, glycolic amide ester analogues. Most glycolic amide esters are readily converted to the parent compound 2 in liver microsomes. It is also stated that the pro-drugs reduce the efflux of protein transporters.
Sulfasalazine is absorbed in the small intestine. All non-absorbed sulfasalazine is consequently metabolized in the colon by bacteria into sulfapyridine which is absorbed into the blood. Because sulfapyridine causes side effects, it is preferred that substantially all sulfasalazine is absorbed in the small intestine and not metabolized in the colon. If more of the applied oral dose of sulfasalazine or a derivative thereof is absorbed in the small intestine, an overall lower oral dose of sulfasalazine (or derivative) can be administered, leading to a lower systemic exposure levels of sulfapyridine, less side effects and thus a more favourable sulfasalazine vs sulfapyridine plasma ratio.
For this to be achieved, the solubility of sulfasalazine needs to be increased without affecting the efflux by the protein transporters, such that sulfasalazine or its derivative can be absorbed in the small intestine without being metabolized in the colon into the side-effect-causing sulfapyridine. This problem is not addressed in the prior art documents mentioned above.
Thus, there is still a need for compounds and/or pharmaceutical compositions containing such compounds, that exhibit the therapeutic efficacy of sulfasalazine itself in the prevention, prophylaxis of progression, and/or treatment of autoimmune diseases, like rheumatoid arthritis or ankylosing spondylitis, with improved gastrointestinal permeability and/or absorption with an ordered enzymatic hydrolysis, i.e. minimal cleavage in the gut lumen prior to absorption.
There is still a need for improved aqueous solubility, improved oral availability and increased plasma levels of sulfasalazine with/without altered plasma levels ratios of sulfasalazine/sulfapyridine and its metabolites. There is a need for improved efficacy/responder rate, improved overall tolerability and/or increased safety, such as reduced gastrointestinal and/or renal toxicity. Preferably the inter- and intra-variability in pharmacokinetics in the inflammatory stage and/or remission stage of autoimmune diseases, like rheumatoid arthritis, can be decreased as well as reducing the effect of co-administration with food. There is a need for reduced dosing frequency, decreased susceptibility to polymorphisms in transporter proteins and/or metabolizing enzymes. This will most likely improve compliance to drug treatment schedules and improved treatments in autoimmune diseases, like small molecule and/or biologic DMARDs and/or glucocorticosteroids. Costs for health care would thus be reduced.